The alignment of the initial position of a drill collar and therefore the initial direction of the drill hole being created is highly important, especially in areas such as mining where the accuracy of drill holes is crucial in ensuring that the correct blasting patterns or that cable bolts etc used to secure the rock face is correctly positioned. A number of differing methods have been used to limited success to ensure that the relative direction (azimuth) and angle (pitch) of a drill hole are correct.
Inaccuracies in azimuth measurements have a huge affect on the accuracy of the drill hole, with an error of 1 degree in azimuth over a 1000 meter drill hole causing and error of 12.3 meters.
Some methods of aligning the drilling collar rely on the use of a compass to measure magnetic north. Azimuth direction is determined as a bearing relative to magnetic north. Compass based techniques are also affected greatly by the type of ore body that is being worked on as well as the closeness of vehicles with steel frames etc.
Other examples of alignment methods have involved the use of surveyors to determine the relative direction (azimuth) and angle (pitch) that a drilling collar rod should contact the rock face to ensure that the hole is drilled in the correct manner. In underground mining operations especially this can be a laborious task as the limited space and distance requires a significant number of calculations to be performed to ensure that the correct azimuth and pitch are set for the drill rig prior to drilling. This requires that the surveyor take measurement after measurement until the crew operating the drill rig have manoeuvred the drill rig into position.
Other alignment methods rely on the use of GPS survey instruments, however, the nature of these instruments mean that they must have ‘vision’ of the global position system satellites and as such are not usable in heavily wooded areas or underground.
It has also been shown that the drill rig itself may block the ‘vision’ of the GPS survey instruments and therefore reduce the accuracy of the measurements produced. One of the many problems faced by GPS systems is they may take up to 10 minutes to determine the azimuth depending upon the number of satellites that are visible. If there are no available satellites no azimuth may be calculated.
Another known problem of GPS survey instruments is that may not be moved once a bearing has been calculated. Therefore it is often necessary for the satellite detection process to be conducted a number of times to ensure correct azimuth alignment before drilling can commence.